On elliptical polarization of the decametric radio emission and the linear mode coupling in the Jovian magnetosphere

We consider the origin of the elliptical polarization of Jupiter's decametric emission as a consequence of the moderate linear mode coupling which takes place in the Jovian magnetosphere outside of the source region. We recognize conditions of emission propagation along the ray path which are necessary for forming of the observed polarization characteristic and show that our model explains the main observed properties of the polarization (value of ellipticity, independence of polarization on frequency and time, stability of polarization from storm to storm). does not need low plasma densities in the emission source and does not contradict the modern knowledge on the decametric emission origin. We show that there is no strong correlation between polarization of the emission at the source and the observed polarization. The observed degrees of (linear and circular) polarization have to be assumed as limits of possible degrees of the polarization of the emission escaping the source region. The value of the ellipticity is defined by the level of the magnetospheric plasma density n(e), in the ''transitional region'', that is in a part of the ray path where the polarization of the normal waves is essentially elliptical. The plasma density in this region is quite low n(e) < 0.4 cm(-3) and is related to the local electron gyrofrequency as n(e) proportional to (f(Be))(nu) where nu similar or equal to 1 divided by 1.8.